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| Arteries and veins |
The lifeline for oxygen and nutrients to the entire body consists of a complex network of tubes called arteries and veins. These deliver nutrients and oxygen to the various parts of the body and collect waste and toxic substance from all over. The flow of blood is regulated by a series of valves in the heart which allow it to flow only in one direction.
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The circulatory system can be divided into two part, i.e., The pulmonary circulation which carries blood to and from the lungs and the systemic circulation which distributes and collects blood from tissues and organs. Arteries are the tubes through which oxygen enriched blood is supplied to all parts of the body. They have thick walls made up of three layers, a smooth inner most layer surrounded by a muscular middle layer and finally a though outer layer.
Arteries divide and branch out into a very narrow network of smaller arteries called Arterioles. These arterioles are connected to a network of Capillaries as they reach their ends. Capillaries are made up of only one layer of cells, they do not have any muscle layer or smooth inner layer. These Capillaries allow oxygen and nutrients to pass through their walls into various parts of the body. Once the blood in the capillaries is exhausted of nutrients and oxygen, it flows into veins. The veins in our body are responsible for carrying blue coloured blood, which lacks nutrients and oxygen, back to our heart from where it is sent to the lungs. Once the blood is enriched with oxygen and nutrients, it is returned tothe heart through coronary arteries from where it is pumped back into the body.
Thus the cycle of constantly replenishing the body with oxygen and nutrients continues. The heart pumps approximately five litters of blood in a minute through the network of arteries and veins thus maintaining an almost constant supply of oxygen and nutrients ot the various parts of the body.
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Medical